Feature spec
Goal: Send a clear invoice after finishing a job.
- Add a client, line items, a due date, and payment instructions.
- Preview the total before exporting a PDF.
- Keep an editable draft if export fails.
App Overview
Marine Navigation - Canada
GPS Marine Charts App offers access to charts covering Canada (derived from CHS data)
$32.99
PRICE
$32.99
No in-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 4.5
2 ratings · Top 15%
Evidence scope: No current overall US chart position is available. Category-chart positions shown in discovery are a separate scope. Revenue is a directional model estimate, not verified earnings.
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Build Kit
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A product spec, screen plans, and build steps for your coding agent.
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What's included17 files
A product spec, phased build plan, differentiation notes, and screen references.
- START_HERE
- AGENTS
- EVIDENCE
- SPEC
- BUILD_PLAN
- DIFFERENTIATION
- skills/
- screens/
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Illustrative example: an invoice app for independent contractors. Your kit is tailored to the app you choose; this is not its generated content.
Screen plan
Invoice editor: Client at the top, editable line items in the middle, total and preview action at the bottom.
States: Empty draft, validation errors beside each field, exporting, and a retry action that preserves the draft.
Differentiate and validate
Hypothesis: Contractors need faster repeat invoices more than more templates.
First experiment: Test duplicating a previous job with five contractors. Watch where they hesitate before expanding the feature set.
The full kit adds a phased build plan, evidence notes, tool prompts, and implementation guidance. It is a plan for your coding agent, not a finished app.
Usage: Mechanics are fair game; never reuse the original name, branding, assets, or verbatim copy.
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Quick prompt
Good fit for mobile-first iOS and Android prototypes with managed app scaffolding.
// RORK SYSTEM PROMPT
Rork plan preview for Marine Navigation - Canada: map the core Navigation workflow, choose the smallest differentiated feature set, define the data and monetization boundaries, then prototype the riskiest user journey first.
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Opportunities
AI-GENERATED OPPORTUNITY HYPOTHESES
These are generated suggestions, not verified review quotations. Check current App Store reviews and speak with users before treating a possible gap as a requirement.
Hypothesis 1
Implement a robust offline maps feature with background downloading.
Assumption to check: Limited offline access to maps and features.
Validate with people who use this workflow before building.
Hypothesis 2
Consider a subscription model or a freemium version with essential features.
Assumption to check: High price point for initial download.
Validate with people who use this workflow before building.
Hypothesis 3
Allow users to customize map styles and layers.
Assumption to check: Lack of user customization for map views.
Validate with people who use this workflow before building.
Hypothesis 4
Enhance POI data with user contributions and detailed descriptions.
Assumption to check: Insufficient points of interest data.
Validate with people who use this workflow before building.
App evidence
Original App Store material. Ratings and screenshots describe the existing app, not proof of demand for your version.
App Store description
GPS Marine Charts App offers access to charts covering Canada (derived from CHS data). Only marine GPS app to have route assistance with Voice Prompts for marine navigation. It has route manager to create new boating routes or import existing GPX/KML routes. It supports Nautical Charts course up orientation. Please visit http://gpsnauticalcharts.com/main/ca-nautical-charts-by-folio.html for complete list. If you don't find the chart for Canada , please contact us at support at gpsnauticalcharts.com. (Includes coverage for Trent Severn Waterway incl. lake Simcoe etc.) * Voice Prompts for marine navigation (requires GPS ) -prompts when approaching a boating route marker -Continous distance and ETA updates -Alerts when sailing/boating off route -Alerts when boating in wrong direction *Route Editing/Creation -Create routes from scratch -Edit existing GPX/KML routes. -Add custom description to any route point. -Drop markers along route. * Offline charts derived from CHS data. -Visually draw area to download -Textual search -Catalog (By state, region and coast guard district) -Charts reprojected for WGS84 datum *Seamless chart quilting of marine charts *Distance Bearing tool *Create custom way points - Using GPS -Select point on map -Manually enter latitude & longitude coordinates *POI layer for marine charts - Overlay POIs - POI list derived from the equivalent ENC and contains all categories including Buoy, Light, Harbour facility, Obstr. *Search POIs/Way points *Pan/Zoom/My Location * Record Marine GPS tracks * View tracks overlay * Live track animation * Track analytics/stats * Export GPX tracks. -Export to SDCard -Share GPX trakcs with friends. * Auto Follow Mode (Course up) -Continuously updates boat's location on chart - Adjustable update frequency Sample Nautical Charts (please visit http://www.gpsnauticalcharts.com/ for complete list) Pacific Coast - Vancouver Island East & West - Haida Gwaii Great lakes Canada and St. Lawrence river Trent-Severn Waterway BALSAM LAKE BALSAM LAKE TO/À BOLSOVER (LOCK/ÉCLUSE) BOLSOVER (LOCK/ÉCLUSE) TO/AU LAKE SIMCOE CAMERON LAKE CHEMONG LAKE ÉCLUSES DE HEALY FALLS LOCKS TO/AU RICE LAKE LAKE COUCHICHING - LAKE SIMCOE TO/À COUCHICHING LOCK/L'ÉCLUSE DE COUCHICHING LAKEFIELD LAKEFIELD LOCK/ÉCLUSE 26 LAKEFIELD TO/À BURLEIGH FALLS LAKE SCUGOG LAKE SIMCOE PETERBOROUGH TO/À LAKEFIELD PIGEON LAKE (NORTH PORTION/PARTIE NORD) PIGEON LAKE (SOUTH PORTION/PARTIE SUD) RICE LAKE RICE LAKE TO/À PETERBOROUGH STONY LAKE STURGEON LAKE Lake Erie \ Lac Erie Lake Huron\Lac Huron Lake Huron\Lac Huron (Southern Portion\Partie sud) Lake Ontario\Lac Ontario Lake Ontario\Lac Ontario, Western Portion\Partie ouest Lake St. Francis Lake Superior\Lac Superieur Vancouver Harbour, Central Portion\Partie Centrale Vancouver Harbour, Eastern Portion\Partie Est Vancouver Harbour, Western Portion\Partie Ouest Vancouver Island\Ile de Vancouver, Juan de Fuca Strait to\a Queen Charlotte Strait of Georgia BARRIE BATAWA LOCK / ÉCLUSE 4 BEAVERTON HARBOUR BENSFORT BRIDGE TO/À PETERBOROUGH BIG CHUTE BIG CHUTE MARINE RAILWAYS BER ROULANT BIG CHUTE TO / À PORT SEVERN BOBCAYGEON - LOCK/ÉCLUSE 32 BOBCAYGEON - LOCK/ÉCLUSE 32 BOBGAYGEON - LOCK/ÉCLUSE 32 BUCKHORN BUCKHORN - LOCK/ÉCLUSE 31 BUCKHORN TO/À GANNON NARROWS AND/ET HARRINGTON NARROWS BURLEIGH FALLS BURLEIGH FALLS LOCK/ÉCLUSE 28 BURLEIGH FALLS TO/À BUCKHORN CAMPBELLFORD LOCK / ÉCLUSE 13 COOK'S BAY AND/ET HOLLAND RIVER COUCHICHING LOCK / ÉCLUSE 42 COUCHICHING LOCK TO BIG CHUTE ÉCLUSE COUCHICHING À BIG CHUTE CROWE BAY LOCK / ÉCLUSE 14 DOURO LOCK/ÉCLUSE 24 FENELON FALLS - LOCK/ÉCLUSE 34 FRANKFORD LOCK / ÉCLUSE 6 GANNON NARROWS TO/À BOBCAYGEON GLEN MILLER LOCK / ÉCLUSE GLEN ROSS LOCK PLEASE NOTE: Continued use of GPS running in the background can dramatically decrease battery life.
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Screenshots
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Build scope
Plan a focused first version with your coding agent. These are planning assumptions, not a delivery guarantee.
Define the first version
Choose one audience and one core workflow. Use the kit to agree on its screens, data, and acceptance criteria before building.
Set boundaries
Decide which secondary features, integrations, and platform support can wait. Your version does not need to reproduce everything in the original.
Check the hard parts
Validate external services, specialist technology, data access, and ongoing costs for your chosen scope.
SUGGESTED BUILD STACK
React Native
Expo
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Zustand
react-native-maps
expo-location
BUILD KIT DIFFICULTY
Intermediate
From the Build Kit assessment.
A reliable timeline needs an agreed scope and a technical check. Ask your agent to estimate the phases in BUILD_PLAN.md after that review.
